As a conventional mobile communication network, there are 2G (2nd Generation) networks such as a GERAN and 3G (3rd Generation) networks such as an UTRAN. In the conventional 2G/3G network, both voice call and data communication services are provided, but 3.9G (3.9 Generation) networks such as an E-UTRAN have been under review to realize a faster high-speed data communication. Since a main object of the 3.9G network is to provide a high-speed data communication service, to perform a voice call by paging the voice call service to a mobile communication terminal resident in the 3.9G network, a mobile communication network in which the mobile communication terminal is resident needs to be transitioned from the 3.9G network to the 2G/3G network to receive the voice call service using 2G/3G service. Such switching of the mobile communication network is referred to as CS fallback (see Non patent Literature 1), and a communication control system compatible with the CS fallback is known.
In a communication control system including the communication control system compatible with the CS fallback, when a call is made from one mobile communication terminal to another mobile communication terminal, at first, acquisition of information specifying a mobile communication switching device (MSC) that manages a called-side mobile communication terminal and routing information such as a routing number allocated to the called-side mobile communication terminal in the mobile communication switching device is performed. Then, a line between both the mobile communication terminals is set based on the acquired routing information, and thereby the voice call is established. At the time of setting the line, in the communication control system compatible with the CS fallback, to increase a communication efficiency, a simultaneous paging to the called-side mobile communication terminal is performed before performing the allocation of a routing number, and so-called pre-paging is performed where the routing number is allocated only in a case where a response is made (see Non patent Literature 2).